Recently, electrical communication systems are demanded of faster communication speed. An OFDM (Orthogonal Frequency Division Multiplexing) system is known as a data communication system which achieves such fast communication speed.
In carrying out data communication, a preamble for performing signal detection, correction, synchronization, etc. is transmitted first. If the preamble is not properly transmitted due to signal distortion or the like, therefore, subsequent data will not be demodulated properly.
It is generally known that the lower the PAPR (Peak-to-Average-Power Ratio) is, the less signal distortion and the higher transmission efficiency a power amplifier has. Since large instantaneous power is generated by multiplexing of subcarriers in OFDM, however, the power amplifier has a high PAPR. In this respect, various techniques to generate a preamble with a low PAPR have been proposed.
For example, International Publication No. (WO) 2006/015108 discloses a technique of generating a preamble with a low PAPR by repeating a CAZAC (Constant Amplitude Zero Auto-Correlation) sequence.